Orthodontics is the branch of dentistry dealing with teeth irregularities and their corrections, such as by means of braces. The primary purpose of orthodontic treatment is to alter the position and reorient an individual's teeth so as to modify or improve their function. Teeth may also be reoriented mainly for cosmetic reasons.
In orthodontic treatment, as currently practiced, it is necessary to affix various orthodontic components to the surfaces of a patient's teeth. (In this specification, we shall only refer to brackets as the orthodontic element or component to be anchored on a tooth's surface, but it is to be understood that this is only by way of example, and the invention applies to all other types of orthodontics elements, mutatis mutandis, such as for example tubes, springs and other appliances.) The location of the bracket on the tooth as well as its orientation is a critical factor in determining the direction of movement of the teeth during the treatment, and accurate placement may ensure that the teeth are aligned with a single bracket bonding treatment. Conversely, less accurate placement of brackets may require repeated treatments, including repeated bonding and wire bending procedures until the final alignment is achieved.
Brackets affixed to teeth surfaces serve to support wires and tensioning springs to exert moments of force acting to move the teeth subjected to these forces to a degree and in a direction causing the teeth to assume a desired posture in the dental arch.
In current orthodontic practice, the orthodontist decides on a general scheme of placing the brackets on the teeth and then attaches each of them to the surface of a tooth, in an exact location and orientation previously decided. Preparatory to an orthodontic treatment, the orthodontist typically prepares a plaster model of the teeth of the treated individual and on the basis of such model, the general scheme of placement of the brackets can be decided. Also, bracket manufacturers typically propose a particular placement position for their brackets, for example that the brackets should be placed within a certain distance from the gingival margin. Such proposals are based on average shapes and sizes of teeth.
A typical treatment plan includes, among other factors, the desired position of each of the force-inducing orthodontic implements on the teeth. The placement of the brackets on the teeth determines the outcome of the above-mentioned movements, e.g. the degree and direction of the teeth movements. Any deviation from the planned position of the brackets affects the outcome of the treatment. Thus, during the process of placing the brackets on the teeth, much effort is made to ensure the accurate positioning of the brackets in accordance with their desired position as determined by the treatment plan.
The brackets are typically placed on the buccal surface of the teeth. At times, it is desired both from a treatment perspective as well as for reasons of external appearance of the individual, to place the brackets on the lingual surface of the teeth. However, by current methods it is difficult to properly position the brackets on the lingual surfaces, particularly in view of difficulties in monitoring the position during attachment of the brackets.
Typically, the following general steps are conducted for properly positioning an orthodontic element such as a bracket on a tooth surface, and then fixing the bracket thereto:
Step I: The orthodontist brings the element, being held by the positioning tool, into proximity of the tooth;
Step II: The orthodontist then positions the orthodontic element on the tooth surface at the site coinciding with its intended position, and disengages it from the positioning tool.
Step III: Finally, the element is affixed to the designated site by a bonding agent.
Special tools are sometimes used for placing the brackets on the teeth, for example as described in U.S. Pat. No. 3,686,762, U.S. Pat. No. 4,424,029, U.S. Pat. No. 4,478,576 and U.S. Pat. No. 6,447,291.
Typically, the bonding of the bracket to the tooth is achieved by using either chemical adhesives or light curing adhesives. Chemical adhesives are typically cured by themselves. The curing begins as the adhesive coming in contact with the tooth surface is completely cured after some self-working time (typically about 1 to 3 minutes).
The difficulty with manual orthodontic procedures, as commonly practiced nowadays, is that they are subject to human error. In the first place, it is very hard to place the bracket where it is desired to be located. Another common difficulty relates to the disengagement of the bracket from the positioning tool, as this process typically causes a slight movement of the bracket on the tooth due to inherent and uncontrolled small human movements.
This difficulty is compounded when the orthodontist must place brackets not only on buccal tooth surfaces but also on lingual surfaces. With existing methods, it is not easy for an orthodontist to properly position brackets on lingual surfaces.
These difficulties are obviated in part by methods disclosed in U.S. Pat. No. 6,334,772 and the systems and devices disclosed therein to carry out these methods. In a preferred method disclosed in this patent, an orthodontic element such as a bracket is properly positioned on a tooth surface, and then the bracket is fixed thereto. A video camera continuously captures an image of the tooth or the element while the orthodontist brings the element into proximity of the tooth using a positioning appliance, and a video monitor displays a real-time image, together with indicators affording information in regard to the position intended for the orthodontic element on the tooth surface. Guided by these indicators, the orthodontist then positions the orthodontic element on the tooth surface at a site that coincides with its intended position, and finally, the element is affixed to this site by a bonding agent.
In WO 03/092532, a positioning appliance adapted to facilitate an orthodontics procedure in which a bracket or other orthodontic component is placed at a desired site on the surface of a tooth and affixed thereto. The appliance in this case comprises a hand-held tubular wand that has a protective sleeve section and a camera section telescoped in the sleeve section. A window is mounted at the front end of the sleeve section and a finger projecting therefrom is adapted to hold the bracket at a position abutting the tooth surface. A camera is housed in the camera section to capture through the window an image of the bracket on the surface of the tooth. One or more light sources are housed in the camera section, for irradiating the bracket and the tooth surface with light detectable by the camera. Additional one or more light sources are housed in the camera section and are capable of irradiates light at a wavelength that can cure an adhesive used for affixing the bracket or other orthodontic component to the surface of a tooth.
A more traditional form of positioning brackets is known as indirect bonding, and is based on forming a tray of a thermoplastic material over a physical model of the teeth on which the brackets have been positioned using a relatively weak adhesive. The brackets may be positioned onto the model in any one of a number of ways, for example as disclosed in U.S. Pat. No. 4,812,118. The tray thus comprises a negative impression of the teeth model, which is very close-fitting with respect thereto, and also has the brackets embedded in position in the tray in their correct positions with respect to the model. The tray can then be removed from the model, taking with it the brackets in the correct relative positions with respect to the negative impressions. The tray is then transferred to the intraoral cavity of the patient, and when properly fitted over the appropriate arch, presents the brackets in ostensibly the correct positions vis-à-vis the teeth. The brackets are simultaneously bonded onto the teeth, which requires all the teeth to be dry and pre-etched, and the tray may then be removed, leaving the brackets in place. This method is commonly practiced, and can be used for both buccal and lingual brackets. Most of the preparatory work is done by a technician rather than the dentist, and the technique results in a shorter installation time than when the brackets are installed manually one at a time, but the technician needs to have a supply of brackets readily available. On the other hand, should one or more of the brackets move during installation, or not be fixed properly onto the teeth, it has to be reset manually without the aid of the tray. In practice, many failures occur due to the imperfect fit between the tray and the teeth, resulting in part due to the dimensional differences between the plaster model and the actual teeth.
Of general background interest, the following references disclose tray-based orthodontic methods and devices.
In U.S. Pat. No. 5,971,754 adhesive is provided in two components, one applied to the teeth and the other to the bracket while embedded in the tray. When the two components come together, a bond forms within a short time period to enable removal of the tray without significantly changing the position of the appliance.
In U.S. Pat. No. 4,501,554, a second, rigid tray is inserted over a first traditional tray that carries the brackets, for stablising the seating of the brackets during seating or drying of the cement securing the brackets.
In U.S. Pat. No. 4,360,341, a variation of the traditional transfer tray is provided, in which the brackets are held in the tray by bracket orienting modules, providing positioning accuracy of the brackets.
In U.S. Pat. No. 6,123,544, brackets are held on arms that are connected to a transfer tray is provided. The arms are aligned with respect to a plaster model of the teeth, and the tray is formed over the arms. The arms are slid away from the model teeth and the assembly is removed from the plaster model. The assembly is then placed into the intraoral cavity, and the arms are retracted into the tray enabling the brackets to contact the teeth at the predetermined positions, where they can be bonded onto the teeth at the contact points. As with the traditional indirect bonding technique, dimensional inaccuracies between the model and the real teeth can lead to inaccurate placement.
In U.S. Pat. No. 5,975,893, aligner-based therapy philosophies and digital imaging/computer-driven rapid prototyping methods are combined, in which a set comprising a plurality of tray-shaped aligners are formed for a patient. Each upper and lower set of aligners (where required) is worn for a period of time. Each aligner in the set biases a patient's teeth toward an ideal occlusion more aggressively than the previous aligner, and typically between 15 to 25 progressive aligners may be used in one treatment. Over a period of time, the sequential and progressively biased positioners move teeth from their initial maloccluded positions to a near finished and corrected state. Each aligner appliance generally comprises a U-shaped tray or shell having a trough that fits over the teeth. The tray is formed by sucking a thermo-formable sheet material over the reset stone model of the patient's dentition, using heat, pressure and a vacuum force, simultaneously. A first initial data set corresponding to the patient's current dentition is determined using a scanning technique. A final digital model of the dentition in its desired set up after treatment is designed. Intermediate digital models between the initial and final models are then created, and positive tooth models are fabricated from the digital models using rapid prototyping techniques. A conventional pressure or vacuum molding machine is used to produce the appliances from each of the positive tooth models.
U.S. 2003/0190575 employs orthodontic aligner elements that are secured to openings in a removable aligner appliance in the form of a tray to exert the desired forces on selected teeth. This enables aligners to be used in the treatment of some orthodontic cases. In addition, the aligner elements are removable or adjustable, and when fitted in the tray, enable the forces to be maintained, changed, or reactivated over the course of treatment.
In U.S. Pat. No. 4,183,141 a rigid cap is formed over the crowns of an idealized model of an arch, and a hollow guide element is fixed with respect to each of the teeth requiring a bracket. Brackets are held at the end of members, each of which slides in the corresponding guide element from a retracted position distanced from the teeth to a deployed position such as to abut the teeth, when the cap is transferred to the patient's arch. In U.S. Pat. No. 5,011,405, U.S. Pat. No. 5,368,478 and U.S. Pat. No. 5,879,158 a digital model of the intraoral cavity is created, and the shape of a positioning device such as a jig is calculated. In U.S. Pat. No. 5,542,842, U.S. Pat. No. 5,863,198, U.S. Pat. No. 4,626,208, U.S. Pat. No. 4,850,864 and U.S. 2003/0224310 various jig configurations are disclosed for positioning brackets with respect to teeth.